The present invention relates to an actuator for transducing a rotational movement into a linear movement.
Actuators, wherein a rotational movement generated by an electric or fluid pressure motor is transduced into a linear movement by means of a ball screw and so on, have been conventionally known.
However, in such conventionally known actuators, transmission gear ratios cannot be changed in accordance with the external load by a simple mechanism.
Accordingly, it has been required to develop an actuator wherein transmission gear ratio can be changed by a simple mechanism in accordance with the external load.
Further, the reducing gear ratios in such conventionally known actuators are small, and accordingly, the amount of linear movement per one revolution of the motor is large. Therefore, a large motor has to be used so as to obtain a desired output force.
Accordingly, in the conventionally known actuators, there are problems that a large space is required for installing such a large motor, that the actuator is heavy because of such a large motor and that the cost of the actuator is expensive since such a large motor is expensive.
In order to overcome the above-mentioned problems, an attempt, wherein the rotation of the motor is reduced by a gear train or an epicycle reduction gear disposed on an output shaft of the motor, has been done so that the reduction gear ratio is made large, i.e., so that the amount of linear movement per one revolution of the motor is made small.
Further, according to the conventional actuators, in order to enhance the reduction gear ratio at the rotational stage, it is necessary to prepare a set of gear trains wherein the diameters of the gears are largely different or to dispose various stages of gear trains. Accordingly, a large space is still necessary, and the weight of the actuator is increased. In addition, there occurs a problem that the construction is complicated when an epicycle reduction gear is used.